FIG. 1 depicts an air-bearing surface (ABS) view of a conventional read transducer 10. The conventional read transducer 10 includes shields 12 and 20, sensor 14 and magnetic bias structures 19. The read sensor 14 is typically a giant magnetoresistive (GMR) sensor or tunneling magnetoresistive (TMR) sensor. The read sensor 14 includes an antiferromagnetic (AFM) layer 18, a pinned layer 17, a nonmagnetic spacer layer 16, and a free layer 15. Also shown is a capping layer. In addition, seed layer(s) may be used.
The pinned layer 17 and free layer 15 are magnetic. The pinned layer 17 may be a single layer or a multilayer. The magnetic moment of the pinned layer is fixed, or pinned, in place by an exchange interaction with the AFM layer 18. The free layer 15 has a magnetization sensitive to an external magnetic field. Thus, the free layer 15 functions as a sensor layer for the magnetoresistive sensor 14. These magnetic bias structures 19 are used to magnetically bias the free layer 15 of the sensor 14. The conventional free layer 15 consists of a multilayer. The layers of the free layer 15 are selected for various purposes. For example, the free layer may include a CoFe layer, NiFe layer and/or other layers. These layers are desired to be selected for, among other purposes, a high magnetoresistance.
Although conventional free layer 15 may function, there are drawbacks. For example, the root mean square variation in the asymmetry (asymmetry a) may be larger than desired. The asymmetry σ may depend upon the material(s) used, the topology of the shield 20 and/or other factors. For example, certain materials such as CoB, which may be desirable for higher magnetoresistance, may exhibit an asymmetry sigma that is larger than desired. As a result, a CoB free layer may not be used for the conventional free layer 15. The conventional free layer 15 may thus have a reduced magnetoresistance or a reduced yield during fabrication due to a large asymmetry a.
Accordingly, what is needed is a system and method for improving the performance of a magnetic recording read transducer.